Soft Walls: Modifying Flight Control Systems to Limit the Flight Space of Commercial Aircraft.

Researchers: Adam Cataldo
Advisor:Edward A. Lee

The Soft Walls project is a technological response to the September 11, 2001 tragedy [1]. The project goal is to design an aircraft control system to enforce government-mandated no-fly zones. The no-fly zones will include major cities, government centers, military installations, chemical and nuclear plants, and critical infrastructure centers. As an aircraft approaches a no-fly zone, the flight control system will force the aircraft away, giving the pilot a sensation of an external force. The no-fly zone boundaries are called Soft Walls, because aircraft are gently diverted as they approach these zones.

In the future, all aircraft are likely to use fly-by-wire systems, where pilot controls are mediated by computers, rather than being mechanically or hydraulically connected to the aircraft control surfaces. We are designing our control system for fly-by-wire aircraft. The aircraft will carry a three-dimensional model of the earth’s surface, augmented with the no-fly zones. The model will change only when the no-fly zones change.  One of our design principles is to give the pilot as much control as possible, subject to the constraint that the aircraft can never enter the no-fly zone.

We have developed several candidate control algorithms for Soft Walls [2]. Our algorithms add a bias to the pilot's control as the aircraft gets near the no-fly zone. The bias is increased and decreased gradually, and the algorithms are provably safe, that is, the aircraft can never enter the no-fly zone. We are now addressing the computational complexity problems that we will need to solve in order to implement such a strategy.

For more information, see the Soft Walls website at

[1] Edward A. Lee, "Soft Walls: Frequently Asked Questions ,"Technical Memorandum UCB/ERL M03/31, University of California, Berkeley, CA 94720, July 21, 2003.

[2] Adam Cataldo, "Control Algorithms for Soft Walls," Master's Report, Technical Memorandum UCB/ERL M03/42, University of California, Berkeley, CA 94720, October 15, 2003.

Last updated 11/01/04